F 240 
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METALLIC FLAVOR IN 
DAIRY PRODUCTS 



A THESIS 

Presented to the Faculty of the Graduate School 

of Cornell University for the degree of 

DOCTOR OF PHILOSOPHY 



BY 

EDWARD SEWALL GUTHRIE 



A Bulletin from the Agricultural Experiment Station of the 
New York State College of Agriculture 



METALLIC FLAVOR IN 
DAIRY PRODUCTS 



A THESIS 

Presented to the Faculty of the Graduate School 

of Cornell University for the degree of 

DOCTOR OF PHILOSOPHY 



BY 

EDWARD SEWALL GUTHRIE 



A Bulletin from the Agricultural Experiment Station of the 
New York State College of Agriculture 






In Exchange 
DEC 4 - 191B 



CONTENTS 

PAGE 

General observations 610 

Period of occurrence 610 

Causes of metallic flavor 61 1 

Preliminary work 612 

Work of other investigators 613 

Nature of medium having metallic flavor in the greatest degree 615 

Factors affecting development of metallic flavor 616 

Relation of fat content to metallic flavor 616 

Relation of acidity to metallic flavor 616 

Temperature in relation to metallic flavor 617 

Effect of cooked flavor in relation to metallic flavor 617 

Method of obtaining a medium for detection of metallic flavor 617 

Bacteria in some metallic-flavored dairy products 619 

Formaldehyde and metallic flavor 620 

Effect of adding pure lactic acid to some dairy products 62 1 

Relation of enzymic growth to metallic' 1 flavor 621 

Number of bacteria in buttermilk before and after development of metallic flavor. 622 

A qualitative study of the bacteria in fresh and in metallic-flavored buttermilk. . . . 623 

Morphological characteristics 626 

Cultural characteristics 626 

Conclusions 627 

Bibliography 628 

Appendix (containing tables) 629 



607 



METALLIC FLAVOR IN DAIRY PRODUCTS 

E. S. Guthrie 

The sale of dairy products depends largely on their flavor. Many 
flavors do not materially affect the sale of dairy goods, but, on the other 
hand, there are several that directly affect their price. Metallic flavor 
belongs to the latter class, and may reduce the price of butter from one to 
two cents a pound. 

Metallic flavor as such was not of great importance until about twelve 
years ago. So far as the writer is able to determine, the first person to 
detect this flavor was B. D. White, who states that in 1901, when he was 
an assistant commissioner on the Dairy and Food Commission of Min- 
nesota, that commission instituted a monthly scoring contest for butter 
in conjunction with the Minnesota Agricultural School. In this contest 
Mr. White criticized the butter, explaining any abnormal flavors or defects 
found. Various flavors were detected, among them a new flavor, which 
was designated as metallic, a curdy flavor, and a feverish, or cowy, flavor. 
It was noticed later, after publication of those criticisms, that other States 
had adopted the same terms in criticizing butter, and the question was 
whether the same flavors were recognized or whether the terms were applied 
to other flavors. Later, however, in monthly scoring contests conducted 
by the National Creamery Buttermakers' Association in connection with 
the United States Department of Agriculture, in which Mr. White was 
critic, the same terms were used, and in that way they were carried through 
the United States rather thoroughly and the various judges who attended 
the different scorings became familiar with them. 

The character of metallic flavor has been determined through personal 
correspondence with noted authorities on butter in this country, and with 
one expert in Denmark, one of the greatest butter countries in the world. 
These men are as follows: Professor Bernhard Boggild, Royal Veterinary 
and Agricultural College, Copenhagen, Denmark; F. W. Bouska, formerly 
professor of dairy bacteriology at Iowa State College, now with the 
Beatrice Creamery Company, Lincoln, Nebraska; C. E. Croomer, manager 
of the butter department of the Fox River Butter Company, Chicago, 
Illinois; C. W. Fryhofer, formerly federal butter expert on the New York 
City market, now in the Dairy Division of the United States Bureau of 
Animal Industry; Professor N. W. Hepburn, University of Illinois; J. C. 
Joslin, formerly federal butter expert on the Chicago market; P. H. Kieffer, 
President of the Gude Brothers Kieffer Company, New York City; Pro- 
fessor C. Larsen. South Dakota State College and Experiment Station; 

609 



610 Bulletin 373 

Professor C. E. Lee, University of Wisconsin; Robert McAdam, formerly 
in charge of renovated butter inspection, Dairy Division, United States 
Bureau of Animal Industry; G. L. McKay, formerly professor of dairying 
at Iowa State College, now secretary of the American Association of 
Creamery Butter Manufacturers; Professor M. Mortensen, Iowa State 
College; Professor A. B. Nystrom, State College of Washington; S. E. 
Thompson, in charge of dairy manufacturing investigations, Dairy Division, 
United States Bureau of Animal Industry; B. D. White, formerly in charge 
of dairy manufacturing investigations, Dairy Division, United States 
Bureau of Animal Industry; Professor J. H. Frandsen, University of 
Nebraska; H. J. Credicott, formerly federal butter inspector on the 
Chicago market. 

According to Fryhofer, Kieffer, Hepburn, McKay, Lee, Thompson, 
and Nystrom, metallic flavor is similar to the flavor of rusty iron. Lee, 
Croomer, Thompson, and Fryhofer state that there is a similarity between 
fishy flavor and metallic flavor. Thompson says: " It is classified as 
fishy, oily, tallowy, etc. I believe, however, that it is safe to say that 
the true metallic flavor is easily recognized by men qualified to judge of 
such things, after they have once become familiar with it." 

The detection of metallic flavor is difficult. In order to determine 
whether there is any uniformity of judgment as to this flavor, the writer 
took a sample of butter pronounced metallic by the butter judges of the 
Department of Dairy Industry at Cornell University, to the National 
Dairy Show, for the criticism of some of the experts already named. 
It was inspected by McKay, Larsen, Thompson, Kieffer, Joslin, Lee, 
Hepburn, Frandsen, and Credicott. Every one of these men said that 
without doubt the flavor was metallic. In each of the criticisms, more 
than one judge examined and criticized the product. In case only two 
judges were present, and one reported in the affirmative while the other 
decided in the negative, the result was counted as negative. But if there 
were four judges, and two pronounced the flavor metallic while the other 
two reported it not metallic, the sample was counted as metallic, with one 
exception. There was no particular reason for this decision, aside from 
the fact that if two judges found metallic flavor it would seem that it must 
be present in a slight degree. When three or five judges made the exam- 
ination, the majority report was taken. 

GENERAL OBSERVATIONS 
PERIOD OF OCCURRENCE 

Croomer and Larsen claim that metallic flavor in butter is found of tenest 
in early spring and late fall ; Kieffer and McAdam say that it is commonest 



Metallic Flavor in Dairy Products 6ii 

in late fall and winter; Hepburn, McKay, and Fryhofer say that it is 
commonest during the hottest time of the year; and Nystrom observes 
that it is commonest in the fall. Thompson says: " The extent or fre- 
quency with which this trouble occurs, I am unable to determine. It is 
apparently confined to no particular section or season, but may occur 
anywhere and at any time." This last opinion — that is, that metallic 
flavor "may occur anywhere and at any time " — is supported by Croomer, 
Hepburn, McKay, Larsen, and Fryhofer. 

CAUSES OF METALLIC FLAVOR 

Joslin and McKay think that pasteurization is a factor in the production 
of metallic flavor in butter. Mortensen and Melick (1912) 1 on the other 
hand, claim that if pasteurization is properly done it prevents the devel- 
opment of the flavor. 

Thompson, Fryhofer, McKay, Joslin, White, and the New York Produce 
Review and American Creamery (19 12), state that there seems to be a 
definite relationship between high acidity and metallic flavor. 

White, McAdam, Croomer, and Kieffer think that metallic flavor is due 
directly to metals. 

Brown (19 12) states that he has known the first of the two churnings 
from a ripener to come out with a fine flavor, and the next one, some two 
hours later and held at a temperature of 46 F., to come out with a bad 
metallic flavor. He says that when there was any metallic flavor at all 
it was invariably the worse in the latter churning. 

Melick (19 1 2) observed that cream seemed to develop metallic flavor 
near its surface. He attributed this to certain atmospheric conditions, 
since no metallic flavor appeared when the vats were carefully closed. 

Boggild writes: " We here in Denmark have for a long time known 
that the same or a similar taste [referring to the metallic flavor] in butter 
can be due to rusty utensils, and in some cases to bacteria, and also that 
the so-called fishy flavor is due to microorganisms." 

Coinciding with Boggild's idea that a microorganism is the cause of 
fishy flavor, the New York Produce Review, and American Creamery 
(19 1 2) makes the following statement: "We will not attempt to assign 
causes for all flavors in butter resembling the 'metallic' Doubtless such 
defects may have a bacterial origin as well as an origin actually associated 
with metals with which the more or less acid cream has come in contact." 

The following extract is from Irish Homestead (1913): 

In some Irish creameries, particularly in those where pasteurization has been 
attempted, regardless of the percentage of fat in the cream, a flavor that somewhat 
resembled " fishiness " was experienced. Although it did not entirely coincide with 
" fishiness," the resemblance was close, but it may be more accurately described as 

1 Dates in parenthesis refer to bibliography, page 628. 



612 Bulletin 373 

a " metallic " flavor, possibly due to some organic cause. This flavor was invariably- 
noticed in butter the cream of which contained over 35 per cent of fat, and it was 
particularly noticeable where the fat content in the cream ran over 40 per cent and up 
to 50 per cent, when the cream was pasteurized. In some cases the flavor was even 
noticeable where the whole milk was not heated beyond 130 F., and where the cream 
was not pasteurized. 

It is, of course, evident that whether milk or cream is pasteurized, the cream for 
buttermaking should not contain more than 33 per cent of fat, and the results, par- 
ticularly as regards the keeping qualities of the butter, are much more likely to be 
satisfactory where a thin cream, not containing over 30 per cent of butterfat, is separated 
and then thoroughly pasteurized, well cooled down, ripened at a moderately low tem- 
perature, with a liberal supply of clean, active starter to an acidity of 0.3 to 0.35, but 
in no case exceeding 0.4. 

In the most progressive and highly successful dairying countries of Europe it is 
the general practice all through the year to separate a thin cream — in most cases 
the cream does not contain over 25 per cent of butterfat, while in one large dairying 
country the cream rarely contains over 20 per cent of butterfat, and pasteurization 
is general among all the creameries 

PRELIMINARY WORK 

The observations on metallic flavor made in the laboratories at Cornell 
University were as follows : 

I. High acid content seemed essential for the development of the flavor. 
Every instance in which metallic flavor was found in the preliminary 

work was in a product of high acidity, and only twice did the writer hear 
of its being noted in sweet dairy products. In one case a milk company 
reported metallic flavor in sweet milk, but it was of short duration. The 
second case was reported by White, who wrote: "I have always found 
the metallic flavor in condensed milk and believe that this is due entirely 
to the raw copper of condensing pans." The writer has never noticed this 
flavor in condensed milk, nor has he detected it in swiss cheese, another 
dairy product made in a copper container. 

The chemist would say that there is far greater probability of a metal's 
being absorbed by an acid solution than by a non-acid one. Nevertheless 
it is true that some dairy products of very high acidity have been held in 
containers with exposed surfaces of metals that easily combine with lactic 
acid to form lactates, such as copper and iron, and have not developed 
a metallic flavor that could be detected by expert judges of that flavor. 
The tin of the starter can in the butter laboratory at Cornell is almost 
entirely off. Starter has been cultivated daily in this can for three or four 
years; it has been carefully examined many times for metallic flavor, and 
this has been present in only a few cases. 

It is possible that electrolytic action plays an important part in the 
production of metallic flavor when the source is directly from metal. 

II. The flavor was most likely to appear during the hottest season. 
It may be that this was noticeable because the degree of acidity of the 

product is likely to be greater when the temperature is high. 

III. A high fat content seemed necessary for the development of the 
flavor, except in the case of buttermilk. 



Metallic Flavor in Dairy Products 613 

These observations, which were made two years before the report of 
Irish Homestead already quoted was published, seemed to indicate 
that metallic flavor developed more rapidly and to a greater extent in cream 
that was rich in butter fat than in cream with a low fat content. The 
flavor was very strong in some samples of soft cream cheese, but was 
never noticed in cottage cheese, which contains practically no butterfat. 
Whenever the flavor was found in whole milk, it was always near the 
surface, in the cream, and it was never observed in skimmed milk. For 
some reason, however, it was often found in buttermilk. With the ex- 
ception of buttermilk, metallic flavor was never found in a dairy product 
that was low in butterfat content. 

IV. The flavor appeared spasmodically. 

Often metallic flavor could not be detected in butter for several weeks, 
and sometimes for many months, after which it suddenly appeared for per- 
haps a few days, or possibly for several weeks. During all this time the 
same utensils were being used on the farms and in the creamery laboratories. 

V. Low temperatures often seemed to make the flavor more apparent. 
The low temperatures in the laboratories may have held in check certain 

organisms that at high temperatures produce sufficiently strong flavors 
to cover the metallic flavor. 

The preliminary observations thus seemed to indicate that there may be 
a cause of metallic flavor other than direct contact of the dairy product 
with metal. In fact, it was quite apparent that there may be a biological 
reason for the development of metallic flavor, for in several instances it 
seemed to increase when the product was not in contact with metal. 

WORK OF OTHER INVESTIGATORS 

Some work has been done of a more scientific nature than that just 
described. The most recent is that of Rogers, Berg, Potteiger, and Davis 
(19 13), who report, besides their own work, researches by several other 
investigators. The following abstract of their bulletin appeared in a 
press notice sent out by the United States Department of Agriculture : 

Some metals either cause or greatly accelerate certain bad flavors in butter, although 
most of the experiments along this line have not included storage butters. Recently 
the scientific staff of the Dairy Division of the Bureau of Animal Industry in the United 
States Department of Agriculture has reported that the presence of very small amounts 
of iron in cream causes certain undesirable flavors to increase in intensity during storage. 
These flavors are often designated by butter experts as " metallic," " oily," or " fishy." 
The injurious effect of iron was found by adding iron in known quantities, varying 
from 1 to 500 parts, to 1 ,000,000 parts of cream. The butter made from such cream 
was compared with that made from cream where all precautions were taken to avoid 
any undue contact with iron during the whole process of butter-making. The butter 
was stored at 6° to io° F., and the quality of the butter was scored by experts at different 
times. In every instance when the butter was scored a few days after making, the 
samples to which iron had been added scored lower than the butter made from cream 
which contained no iron. This held true in most cases on the second and third scoring, 



614 Bulletin 373 

which occurred at intervals varying from 20 to 187 days. The most noticeable feature 
was the rapid development of bad flavor in the butter containing the iron. When 
both the control and the experimental butter became fishy it was noticed that the 
control butter was the last to become so. There was a marked oily flavor present 
in most samples that subsequently became fishy. Only a small proportion of the iron 
added to the cream was found in the butter, the remainder having been taken up by 
the buttermilk and wash water. 

Butter was also made from cream which had stood in rusty cans, and in every case 
this butter had a peculiar taste and was easily picked out from all other samples. The 
buttermilk also had a decided metallic taste. 

The influence of copper on the flavor of butter was studied in a similar manner, 
and it was found that copper, even in small quantities, seemed to cause more marked 
changes of flavor in butter than did the iron, with a decided tendency toward a fishy 
flavor in storage. Two experiments showed very plainly the harmful effect of using 
poorly tinned pasteurizers, even though the cream came in contact with the copper 
surface for only a few seconds, for, aside from this, all other conditions were exactly 
alike during the complete process of butter manufacture. 

This work shows that if cream is kept in rusty cans or comes in contact with iron 
or copper at any time during the process of butter-making it may take up iron or copper 
from rusty cans, exposed bolt heads, or other metal parts of pasteurizers or churns, 
in sufficient quantities to affect the flavor of storage butter. Though there is nothing 
to show that the nature of the flavor is appreciably changed, it does demonstrate very 
clearly that the rate of development of the undesirable flavor is greatly accelerated 
during storage by very small quantities of either iron or copper. 

Golding and Feilmann (1905) think that microorganisms may be the 
fundamental cause of metallic flavor. However, they attribute the cause 
largely to contact of the product with exposed surfaces of copper. They 
found that milk passed over an untinned copper cooler took up 2.5 parts, 
of copper in 10,000,000 parts of sweet milk, and, though the characteristic 
flavor was not at once apparent, it invariably was perceptible in about 
eighteen hours at room temperature. They observed that air aids greatly 
in the solution of copper in milk. Clean copper gauze fixed on the surface 
of some milk in a beaker and left for one week resulted in the solution of 1 2 1 
parts of copper in 1,000,000 parts of milk. At the bottom of the beaker 
only 48 parts per million were dissolved. They say: 

The chemistry of the flavour is still only a matter of speculation, but similar flavours 
can be produced by other oxidising agents, such as potassium permanganate, ferric 
chloride and hydrogen peroxide. 

A large number of organisms were isolated from the different samples of milk which 
had developed the characteristic flavour; but none of them developed the flavour in 
milk which had been sterilised by heat. When, however, the influence of the copper 
had been discovered, the experiments were repeated, and the flavor seemed to be de- 
veloped by certain organisms, but was rather masked by the well-known taste of the 
sterilised milk. 

************* 

The bacteriological investigations of a rather indefinite flavour, which is largely 
masked in heated milk, cannot be very satisfactory, but it seems certain that micro- 
organisms are not without influence in some direct or indirect way. 

In the discussion that followed this paper (read before the Society of 
Chemical Industry), H. Droop Richmond, a well-known English chemist, 
said that he had for some years thought the taste complained of was not 
due to copper, because it was some time before it came out ; he believed it 



Metallic Flavor in Dairy Products 615 

was due rather to microorganisms. The paper, however, showed that both 
were active agents. Mr. Richmond had succeeded in finding a liquefying 
microorganism which he had no doubt was similar to the one just shown 
by the authors. The metallic taste was found chiefly in winter, in milk 
that had been pasteurized; in summer it was not so marked, and neither 
was it so marked in the presence of a large number of lactic organisms. 
Mr. Richmond succeeded in getting rid of the taste by finding where the 
organisms existed. 

There seems to be no doubt, therefore, that metallic flavor is caused by 
the direct absorption of metal by milk or cream. It is apparent also that 
more or less work has been done, the results of which, coinciding with 
some of the general observations noted in preceding pages, indicate that 
bacteria may cause the flavor. 

NATURE OF MEDIUM HAVING METALLIC FLAVOR IN THE 
GREATEST DEGREE 

The senses of taste and smell are the only means by which metallic 
flavor can be detected, and it is to be expected that the nature of the 
medium will influence these senses. It has already been stated that a high 
proportion of butterfat seems necessary for the production of metallic 
flavor, except in the case of buttermilk. Cream often showed only a 
trace of the flavor, but the flavor of buttermilk from the same cream 
churned in a glass bottle was very metallic. This showed that either 
the serum was more easily tasted than was the cream because of its physical 
nature, or else it was more metallic in flavor. The former is probably 
true, and the latter, according to work done and recorded later in this 
bulletin, is also true. 

A few experiments were made in separating the water and the solids in 
buttermilk by centrifugal force. Buttermilk was put into a glass tube 
and placed in a centrifuge. After separation, the water and the solids 
were carefully examined in order to determine which had the more metallic 
flavor. No difference was noticed. 

The metallic flavor appears to be volatile. In buttermilk that had 
developed the flavor in a glass bottle, the metallic odor was very noticeable 
immediately after the removal of the stopper. Several attempts were 
made to concentrate the flavor. Portions of the metallic buttermilk were 
distilled, and the distillate was then condensed by evaporation, but no 
metallic flavor was apparent. Instead the flavor was flat and oily. 

It is difficult to explain why metallic flavor develops to a greater degree 
in buttermilk than in any other dairy product. As has already been 
stated, a high proportion of butterfat is generally essential for the pro- 
duction of metallic flavor, and ordinarily it does not develop in serum 



616 Bulletin 373 

alone, such as skimmed milk; but in buttermilk, which contains only a 
little more fat than does skimmed milk, the flavor becomes very pronounced. 
It was thought that there might be a relation between the acids of the but- 
terfat and the metallic flavor. For example, some of these volatile acids 
might be in buttermilk and not in skimmed milk. Samples of butyric, 
caproic, caprylic, palmitic, stearic, and oleic acids were obtained, also 
propionic acid, which is lower in the fatty acid series, and succinic acid, 
which is a dibasic organic acid and may be found in dairy products. No 
sign of metallic flavor, however, could be detected in any of these acids. 

FACTORS AFFECTING DEVELOPMENT OF METALLIC FLAVOR 
RELATION OF FAT CONTENT TO METALLIC FLAVOR 

Twenty-six samples of skimmed milk were placed in sterilized glass 
bottles and inoculated with buttermilk having metallic flavor. Only 
two of the samples showed any indication of metallic flavor, and in these 
the flavor could hardly be called metallic. 

Forty-three samples of whole milk were treated in like manner. Only 
four developed metallic flavor, and in these the flavor was noticeable 
only in the cream on the surface. 

Sixty-six samples of cream were inoculated with buttermilk having 
metallic flavor, and held in sterilized glass bottles. Seventeen of the sixty- 
six samples developed metallic flavor, a few of these being strongly metallic. 
In addition to the sixty-six samples, five samples of cream were allowed to 
stand at room temperature without inoculation. Four of these developed 
metallic flavor. The five samples were obtained from a source in which 
metallic flavor had previously appeared. 

It has already been stated that metallic flavor has not been observed in 
cottage cheese, but that it is often very strong in soft cream cheese. It 
therefore seems apparent that the presence of fat in fairly large quantities 
is necessary for the flavor to develop. 

RELATION OF ACIDITY TO METALLIC FLAVOR 

Samples of buttermilk were placed in sterilized glass bottles and metallic 
flavor was allowed to develop. Of sixty-nine samples the acidity was 
noted in nineteen, and of these nineteen samples the acidity of six samples 
was taken both before and after the flavor became metallic. The results 
are shown in table 1 . 2 The acidity of all the nineteen samples after metal- 
lic flavor developed varied from 0.69 to 0.83 per cent. 

In many other samples of which no record was kept, it was possible to 
detect metallic flavor when the buttermilk became highly acid, and not 
until then. 



2 Tables referred to in this bulletin are printed in the appendix, pages 629 to 643. 



Metallic Flavor in Dairy Products 617 

TEMPERATURE IN RELATION TO METALLIC FLAVOR 

It was thought that metallic flavor developed more rapidly at low 
temperatures — as, for example, in the refrigerator — than at room temper- 
ature. A series of experiments was conducted in order to determine this 
question. The results are given in table 2 (page 629). 

The effects of different temperatures on the flavor varied but little. 
It is interesting to note, however, that some of the room-temperature 
samples showed a more pronounced metallic flavor than was found at the 
low temperatures, although probably the average of the low-temperature 
samples had a stronger flavor than the average of the room-temperature 
samples. 

It is probable that other flavors develop at higher temperatures, which 
have a tendency to hide metallic flavor if it is present. However, if the 
product is tasted at the proper time, there is no doubt that metallic flavor 
will be found in no uncertain degree. 

EFFECT OF COOKED FLAVOR IN RELATION TO METALLIC FLAVOR 

As already noted (page 611), there is a difference of opinion regarding 
the effect of pasteurization on development of metallic flavor. In the 
course of this study several attempts were made to produce the flavor 
in pasteurized or sterilized cream, but since the cooked flavor masked 
most of the other flavors it was very difficult to reach any definite conclu- 
sion. One hundred and sixty-three attempts were made to produce metal- 
lic flavor in either sterilized or pasteurized cream, by inoculation with 
metallic-flavored buttermilk. In only two of the samples was the metallic 
flavor distinguished from the cooked flavor. 

METHOD OF OBTAINING A MEDIUM FOR DETECTION OF 
METALLIC FLAVOR 

In order to obtain a medium for detecting metallic flavor in dairy prod- 
ucts, the common method of sterilization of cream by heat was first 
tried. Cream having a butterfat content of about 30 per cent was ster- 
ilized in the steam bath on three consecutive days, but the cooked flavor 
so masked the other flavors that this method could not be used. Lower 
temperatures were then tried. About 20 cubic centimeters of cream 
having a butterfat content of 30 per cent was put into test tubes. The 
wire container, with the tubes, was placed in water, and the temperature 
was raised to 140 F. and maintained at that point for twenty minutes. 
The process was repeated on three consecutive days. One hundred and 
three test tubes of this sterilized cream were then inoculated with metallic- 
flavored buttermilk; only two showed metallic flavor. In many cases 
the judges thought they could detect a slight metallic flavor or one similar 



6i8 Bulletin 373 

to it, but they were not certain, for the cooked flavor was present to a 
considerable degree. 

Germicides were next considered, but nothing tasteless could be found. 
It was thought that volatile antiseptics might be used, such as ether or 
chloroform. Heat could then be applied to eliminate the antiseptics, 
but the physical properties of the cream were changed, this assuming a 
greasy appearance and an oily taste. 

The only alternative seemed to be raw cream, and therefore milk was 
obtained directly from the cow. At first it was milked into large sterilized 
glass bottles and allowed to stand for twenty-four hours. At the end of 
that time the serum in the bottom of the bottles was drawn off with a 
sterilized pipette. Several trials were run, the cream being divided into 
portions of 50 cubic centimeters and put into smaller sterilized glass 
bottles. Each portion was inoculated with from one-half to one cubic 
centimeter of metallic-flavored buttermilk. Of twenty-three samples 
of this cream, eight developed metallic flavor. 

Two objections to this method of separation became apparent. First, 
the cream was not sufficiently rich in butterfat, for it is not possible to 
obtain cream with a high fat content when the separation is done by any 
of the gravity methods. This high fat content is one of the essential 
conditions for the development of metallic flavor. Secondly, too much 
bacterial growth took place during the creaming process, which made the 
cream an uncertain medium for the study of the organisms that pro- 
duce metallic flavor. 

An attempt was next made to use cream from the market milk labora- 
tory. This cream was standardized to a fat content of 32 per cent, and 
from this standpoint it was ideal. One hundred and seven samples of 
this cream were put into sterilized glass bottles. Each sample consisted 
of about 50 cubic centimeters of cream and was inoculated with from 
one-half to one cubic centimeter of metallic-flavored buttermilk. Thirty- 
nine of the samples showed metallic flavor. Two sets, of six samples 
each, were carefully tasted immediately after inoculation. Not a trace 
of metallic flavor could be detected. As additional evidence that this 
cream was not affected by contact with tin, it should be noted that not a 
check sample showed metallic flavor. 

There was one factor in connection with the cream from the market 
milk laboratory that made it unsatisfactory: it contained a number of 
microorganisms which made interpretation of the results difficult. When 
metallic flavor was found in these samples, the question could well be 
asked, Was the flavor produced by organisms in the metallic-flavored 
buttermilk with which the cream was inoculated, or was there an asso- 
ciative action between the organisms in the buttermilk and those already 
in the cream? 



Metallic Flavor in Dairy Products 619 

In the search for better cream it was learned that the milk from a certain 
cow in the university herd usually showed the low bacteria count of from 
two to three hundred per cubic centimeter. In fact, the analysis of one 
milking showed only six bacteria per cubic centimeter. It was possible 
to hold the cream from this cow for about forty-eight hours at room tem- 
perature without much change. It therefore seemed that the associa- 
tive action of the bacteria in the metallic-flavored buttermilk and in this 
cream would be almost negative. Therefore the remainder of the cream 
medium was obtained by taking milk from this cow, milking into a ster- 
ilized covered pail. The milk was taken immediately to the laboratory 
and separated in a sterilized separator, the cream being caught in ster- 
ilized glass bottles. As soon as the separation was complete, the cream was 
divided into portions of 50 cubic centimeters in sterilized glass bottles, 
and immediately inoculated. 

BACTERIA IN SOME METALLIC-FLAVORED DAIRY PRODUCTS 

The first series of samples to be examined for bacteria consisted of me- 
tallic-flavored butter. Five samples were plated in lactose agar and a brief 
morphological and cultural study was made, with the following results : 

Sample 1. On one plate of the first sample there were twenty brown 
colonies in tetrads, and several milky white colonies. These organisms 
were micrococci. A few small acid colonies and one of Oidium lactis were 
found. 

Sample 2. The second sample contained several spreaders, and one 
milky white colony with a regular edge which was a streptococcus. There 
were two chalky white colonies with very irregular edges and a wrinkled 
surface. These organisms were short, rod-shaped, and with rounded ends, 
and were nonmotile. Several small cream-colored punctiform colonies 
were present, which under the microscope appeared very much like Oidium 
lactis but were much smaller. Seventy-five Oidium lactis organisms were 
found. 

Sample 3 . In the third sample eight cream-colored colonies were found 
which were diplococci. There were two small brown colonies of staphy- 
lococci, and a few milky white colonies of bacteria which were nonmotile, 
short, and rod-shaped, with rounded ends. 

Sample 4. In the fourth sample there were several small punctiform 
cream-colored colonies, three milky white colonies which were micrococci, 
and thirty colonies of Oidium lactis. 

Sample 5 . The one plate of the fifth sample that could be used con- 
tained only seven colonies. All were white and spreading, and the organ- 
isms were nonmotile, short, and rod-shaped. 

No one organism was present in all the five samples. The organism that 



620 Bulletin 373 

was most abundant was Oidium lactis, but this was found in only three of 
the samples. To determine the effect of Oidium lactis in cream, six samples 
were inoculated with this organism ; none of these developed metallic flavor. 

Since it was possible to obtain metallic flavor almost at will in the but- 
termilk of the university laboratory, a study was made of the milk and cream 
delivered at one of the six receiving stations. A sample of each patron's 
milk or cream was put into a sterilized glass bottle. Room temperatures 
were used for incubation. The results are given in table 3 (page 630). 
It is seen from the table that two samples, one of cream (no. 21) and one 
of whole milk (no. 62), had metallic flavor. The flavor was stronger in 
the cream sample, and this was plated in order to determine whether or 
not the organism Oidium lactis was present — the idea having been suggested 
by Bouska (page 609) that Oidium lactis might be the cause of metallic 
flavor. A large number of colonies of Oidium lactis were found. 

The results of a second study of the milk and cream at the same station 
are given in table 4 (page 631). Again sample 21 had metallic flavor, 
but sample 62 showed no trace of it. Another cream sample, however, 
no. 25, was metallic in flavor. 

The impression is somewhat prevalent that cream of a high grade does 
not develop metallic flavor. It should be noted that in both studies 
sample 21 when fresh was judged as good. On the other hand, sample 
62 was only fair in flavor when fresh, and soon turned to bad. Later 
four samples of cream, all of good flavor, were taken on different days from 
the patron who supplied sample 2 1 . All these samples developed metallic 
flavor. It therefore seems that the flavor may develop in either good or 
poor cream. 

In the experiment reported in table 4, an examination was made of 
all the samples for the presence of Oidium lactis. It is seen in the table 
that twenty of the thirty-two samples contained this organism. It 
should be noted, however, that the two samples which were metallic in 
flavor contained no Oidium lactis. 

FORMALDEHYDE AND METALLIC FLAVOR 

Formaldehyde is considered a very efficacious disinfectant. It kills 
not only bacteria, but also their enzymes. A study was made of the 
effect of formaldehyde on the development of metallic flavor in buttermilk. 
Samples of buttermilk that was not metallic in flavor were taken fresh 
from the churn and immediately treated with formalin (a solution con- 
taining from 37 to 40 per cent of formaldehyde). The results are shown 
in table 5 (page 632). It is seen from the table that in only a small 
proportion of the samples did metallic flavor not develop. Of- the forty- 
one samples treated, thirty-five were metallic in flavor. 



Metallic Flavor in Dairy Products 621 

In order to determine the efficiency of the formalin a bacteriological 
examination was made, with rather surprising results. All the samples 
were incubated at room temperature for two days. On some of the 
plates there were many organisms. The results are shown in table 6 
(page 633). These results indicate that formalin does not kill all the 
bacteria in buttermilk ; it does, however, undoubtedly retard their growth. 

EFFECT OF ADDING PURE LACTIC ACID TO SOME DAIRY 
PRODUCTS 

Inasmuch as metallic flavor was developed in sterilized glass bottles 
in the presence of formalin, a substance that either kills or checks the growth 
of microorganisms and possibly checks enzymic growth, the question 
arose, What would be the effect of adding pure lactic acid to fresh butter- 
milk that is not metallic in flavor, or to skimmed milk? The reason for 
such a question was that a flavor of metallic nature might be produced 
by the action of the lactic acid and the serum of the buttermilk under 
certain conditions. Several experiments were run with varying quantities 
of pure lactic acid, but there was no trace of metallic flavor. 

RELATION OF ENZYMIC GROWTH TO METALLIC FLAVOR 

A limited study was made of the relation of enzymic growth to metallic 
flavor. The first problem in this connection was to find a solution that 
would effectually check the growth of the microorganisms and yet permit 
the enzymes to grow, and would not impart to the medium a flavor that 
would make detection of the metallic flavor difficult or impossible. No 
solution was found that left the metallic flavor clear and distinct. One 
compound, however, could be so managed as to make possible the detection 
of metallic flavor in at least a small number of samples. 

Three per cent by measure of toluene was first used in buttermilk. 
Toluene is considered one of the most effective substances to check the 
growth of bacteria and still permit enzymic action, but the flavor is so 
sharp that detection of other flavors is impossible. The toluene could 
not be removed by heat, for its boiling point is no° C. and if such a tem- 
perature were used the buttermilk would be scorched. Four unsuccessful 
attempts in the use of toluene were made. 

The next agent to be tried was chloroform, which has a boiling point 
of 6 1. 2 C. and can therefore be readily evaporated at a temperature 
that does not affect the flavor of buttermilk. According to Harding 
and Van Slyke (1907)-, 2.5 per cent of chloroform will check the growth 
of any microorganism in milk and not retard enzymic growth. In the 
experiments with chloroform, 50 cubic centimeters of fresh buttermilk, 



622 Bulletin 373 

not metallic in flavor, was placed in each of two sterilized glass bottles. 
One of these bottles was held as a check. In the other, 2.5 per cent 
by measure of chloroform was added. The mixture was then thoroughly 
shaken and kept at room temperature. The chloroform had a tendency 
to settle to the bottom; consequently it was necessary to shake the mixture 
several times in a day. At the end of two days about 20 cubic centimeters 
of the chloroformed buttermilk was put into a beaker and placed in water 
over a bunsen burner. The temperature of the water was maintained 
at from 62 ° to 65 C. until all the chloroform was evaporated. This 
process required about twenty minutes. Fourteen trials were made, 
in two of which a slight metallic flavor seemed to have developed. A 
sweetish flavor, resulting from the chloroform, always remained. In every 
case the check sample became metallic in flavor. 

This study was not satisfactory, largely because of the difficulty in 
distinguishing the flavors after the buttermilk had been treated. Never- 
theless, the indications were that metallic flavor might be produced by 
enzymic action. 

NUMBER OF BACTERIA IN BUTTERMILK BEFORE AND AFTER 
DEVELOPMENT OF METALLIC FLAVOR 

It was thought best, among other things, to determine the number 
of bacteria in the buttermilk before and after development of metallic 
flavor, for there were strong indications that the flavor might be caused 
by bacteria. Lactose agar and lactose gelatin were the media used. 
As has already been stated, high acidity seemed essential in the develop- 
ment of the flavor, and therefore media of different acid content were 
used. The regular lactose agar and lactose gelatin were prepared with 
an acidity of +1.5 (equivalent to 0.135 P er cent lactic acid, which is 
a little lower than the acidity of sweet milk), and the other agar and 
gelatin were prepared with from 0.75 to 0.8 per cent of lactic acid 
(which is about the same as the acidity of the buttermilk that showed the 
strongest metallic flavor). 

Much difficulty was experienced in preparing the agar and the gelatin 
with the high acidity of from 0.75 to 0.8 per cent. At first the acid 
was added in the same manner as in making the regular medium, but 
when the agar was sterilized it would not congeal. After several un- 
successful attempts the writer learned from Bouska (page 609) that the 
addition of- tartaric acid before sterilization prevents solidification of the 
agar, but if the acid is added after sterilization it does not have this effect. 
This method was tried with the lactic acid, with satisfactory results. 

The question of sterilization of the lactic acid solution was next consid- 
ered, but on bacterial analysis it was found that the solution was already 



Metallic Flavor in Dairy Products 623 

sterile. The strength of this solution was nine-tenths of normal. When 
one cubic centimeter was placed in ten cubic centimeters of the agar or 
the gelatin, the percentage of lactic acid was from 0.75 to 0.8 per cent, 
depending on the age of the medium and therefore on the amount of evap- 
oration that had taken place — it having been held for a part of the time 
at room temperature. 

A study of table 7 (page 634), showing the number of bacteria in the 
buttermilk before and after metallic flavor developed, shows certain facts. 
First, there is no direct relationship between the number of bacteria and 
the metallic flavor, for in sample 1 only about 5,000,000 bacteria were 
found in the metallic-flavored buttermilk as against over 328,000,000 
in sample 13. Secondly, there may be an increase or a decrease in the 
number of bacteria from the fresh to the metallic-flavored stage of the 
buttermilk; six samples show an increase and ten a decrease when grown 
on plain lactose agar, while in the high-acid agar three samples decreased 
in number of bacteria and eight increased. Thirdly, only a small pro- 
portion of the bacteria that grow in the lactose media with an acidity 
of +1.5 will grow on the lactose media with from 0.75 to 0.8 per cent 
of lactic acid. 

It is seen in table 7 that eleven samples of buttermilk were plated on 
both agars at room temperature before and after the buttermilk became 
metallic in flavor. The ratios of the numbers of bacteria in these eleven 
samples in the two agars are- shown in table 8 (page 635). Even though 
these ratios show a greater proportion of bacteria growing on the high- 
acid agar in the metallic-flavored buttermilk than in the fresh buttermilk, 
this does not seem particularly significant, for table 8 shows that there 
was great variation. Further, one would naturally expect to find a greater 
proportion of the bacteria producing metallic flavor growing on the high- 
acid medium, for metallic-flavored buttermilk, as already stated, is always 
high in lactic acid, and this of itself would tend to eliminate other bacteria 
that could not exist in a high-acid medium. 

A QUALITATIVE STUDY OF THE BACTERIA IN FRESH AND IN 
METALLIC-FLAVORED BUTTERMILK 

At the same time that the bacteria in the fresh and the metallic-flavored 
buttermilk were counted, a study was made of their action on litmus 
milk, which was prepared in the following manner: A litmus solution 
with an acidity of +1.5 was added to fresh skimmed milk at the rate of 
1.5 cubic centimeters of litmus solution to 10 cubic centimeters of skimmed 
milk. After being thoroughly mixed, the litmus milk was put into ster- 
ilized test tubes, about 10 cubic centimeters in each tube. It was then 



624 Bulletin 373 

sterilized in the steam bath, by the intermittent method, on three con- 
secutive days. The tubes were kept in the bath for thirty minutes each 
day. 

The litmus milk was inoculated from the plates from which the counts 
were obtained as recorded in table 7 . The inoculation consisted in trans- 
ferring a part or the whole of an individual colony to a single tube of milk, 
the transfer being made with the end of a platinum needle pounded flat 
and bent in the form of a short hook. The number of tubes inoculated 
from one plate varied from 10 to 146, as seen in tables 9 and 10 (pages 636 
and 637). The tubes were held at room temperature, and records were 
taken on the second, fifth, and fourteenth days after inoculation. The 
classes recorded were acid producing, acid producing with coagulation, 
peptonizers, alkaline, and inert. 

If the group classed as peptonizers had appeared in larger numbers, 
it would have been necessary to hold the tubes longer than two weeks in 
order to give sufficient time for the peptonization process. But because 
of the probability that this group, which was very small, did not cause 
metallic flavor, the final record was taken on the fourteenth day. 

The results of the study of the organisms transferred from agar of the 
lower acidity are shown in table 9 (page 636). The table shows that on 
the fourteenth day the average percentage of bacteria that produced 
acid and caused coagulation was 72.95. In the inert class there was an 
average percentage of 18.58, and in the group that showed acid produc- 
tion only there was an average percentage of 7.29. 

Very different results appear in table 10 (page 637), which shows the bac- 
terial action when a high-acid medium is used. The group showing 
acid production alone was much larger than for the normal medium, but 
in only one sample was there any coagulation, demonstrating that the 
bacteria which cause coagulation do not grow in a high-acid medium. 

It is noticeable that the percentages of bacteria in all the groups as shown 
in both tables vary considerably. It is possible that in the case of the 
inert group some of the tubes were not inoculated. With the normal 
medium, however (table 9), the percentage of the inert group was small 
with the exception of two samples, leading to the conclusion that the 
number of unsuccessful transfers was small. Granting that all the tubes 
were properly inoculated, it is seen that in the high-acid agar on the 
fourteenth day an average of 56.79 per cent of the bacteria had not grown 
in litmus milk, while in the acid-producing group there was an average 
percentage of 38.93. 

Because of the fact that metallic flavor was found only in dairy products 
of high acid content, it was natural to first study the group of bacteria 
that grew well on the high-acid medium and the group that would produce 



Metallic Flavor in Dairy Products 625 

acid. One set of twenty samples of cream was inoculated. The cream 
was examined when ripe, and the flavor was pronounced bitter. It did not 
resemble metallic flavor in the slightest degree. 

The next bacteria to be studied were those of the group producing acid 
with coagulation. Twenty tubes were taken at random from about 
two hundred containing these bacteria. Samples of cream, each con- 
sisting of 20 cubic centimeters, were inoculated respectively with \ cubic 
centimeter or less of the milk coagulum from each of the tubes. The 
samples of inoculated cream were held for thirty-six hours at room temper- 
ature, and were then placed in the refrigerator for another thirty-six 
hours before being judged. 3 

In the first trial of this experiment (table n, page 638), three or more of 
the five judges pronounced thirteen of the twenty samples metallic in 
flavor. In the second trial (table 12, page 638), only two of the twenty 
samples were pronounced metallic in flavor by two of the three judges. In 
the third trial (table 13, page 639), three of the twenty samples were pro- 
nounced metallic in flavor by three of the four judges. 

These results were not satisfactory, for there was considerable difference 
of opinion. In many cases there was a flavor which was somewhat similar 
to metallic flavor and yet could not be termed metallic. Some of the sam- 
ples had seemingly passed through the metallic-flavored stage, and other 
flavors had developed which masked the metallic flavor. 

Because of the difficulty in detecting the flavor, another trial was made. 
This time about 150 cubic centimeters of cream was used. All the sam- 
ples were inoculated and ripened in the same manner as in the preceding 
trials. They were then churned by hand in the sample bottle in which the 
cream was ripened. 

Eighteen of these twenty samples (table 14, page 639) were pronounced 
metallic in flavor by three or more of the five judges. The remaining 
two samples seemed to have the flavor to a very slight degree, but it was 
not sufficiently strong to warrant judging the samples as metallic-flavored. 
It should be noted, however, that sample 5 was in the first trial pro- 
nounced metallic in flavor by three of the five judges; and in the case of 
sample 7 , in the first and fourth trials one judge pronounced the flavor 
metallic and another considered it doubtful, in the second trial the sam- 
ple was pronounced metallic in flavor by the judge who raised a question 
about it in the first trial, and in the third trial two of the four judges 
placed it with the metallic-flavored samples. It would therefore seem that 
these samples also probably had metallic flavor in a slight degree. 

3 The judges were: H. L. Ayres, extension instructor, and instructor in butter making in the winter 
course, at Cornel! University; H. W. Middaugh, superintendent of milk supply, formerly head butter 
niaker; W. A. Luce, head butter maker; H. M. Pickerill, instructor in bacteriology, formerly assistant 
in the butter laboratory; and the writer. 



626 Bulletin 373 

A year after this work was done, a sample of buttermilk was obtained 
from the creamery laboratory and a study of the bacteria contained in it 
was made in the same manner as were the previous studies. Samples 
of cream were also obtained, in the manner described on page 619. About 
1 50 cubic centimeters of cream was inoculated from a tube of the bacteria 
producing acid with coagulation. The cream was churned when ripe, 
and the flavor of the resulting buttermilk was studied. 4 

The results of the experiment (table 15, page 640) were peculiar and 
uncertain. In the first place, the check sample was pronounced metallic 
in flavor by all the five judges, while four of the sixteen inoculated samples 
showed no trace of metallic flavor. It must be remembered that the check 
sample was not sterile and could not be made sterile without affecting the 
flavor of the cream. Under such conditions it is to be expected that a 
check sample would occasionally show metallic flavor. 

Another experiment was made with thirteen inoculated samples. 5 In 
this experiment the check sample was not metallic in flavor. Three of 
the inoculated samples (table 16, page 641) were pronounced metallic 
in flavor by four or more of the eight judges. With three exceptions, all 
the other samples were classed as metallic-flavored by at least one of the 
eight judges, and in the case of one of the exceptional samples four of the 
judges raised the question as to whether or not the flavor was metallic. 

MORPHOLOGICAL CHARACTERISTICS 

The bacteria in each culture were carefully studied under the micro- 
scope. They were found to be nonmotile, very short, and rod-shaped, 
appearing singly and in chains of two or more. A few of the chains con- 
tained seven or eight bacteria. They appeared to be the same as the well- 
known bacteria found in milk — the Bacterium lactis acidi group ; if there 
was any difference it was in size, these appearing to be a little larger than 
those representative of the group, but the difference was slight. 

CULTURAL CHARACTERISTICS 

In all the tubes of litmus milk coagulation took place, and all samples 
showed growth without liquef action on gelatin. These are the two cul- 
tural characters that have generally been used to identify members of the 
Bacterium lactis acidi group. 

Further study of cultural characteristics seemed necessary. It has been 
usually considered that certain zymogenic bacteria can be more easily 
recognized by their growth on the various sugars and closely related sub- 

» The judges were the same as in the earlier work, with the addition of Professor N. W. Hepburn, of 
the University of Illinois. 

6 Additional judges in this experiment were G. C. Supplee. assistant in the butter laboratory; and V. R. 
Jones, assistant in the testing laboratory. 



Metallic Flavor in Dairy Products 627 

stances than on any other media. Consequently a study was made of 
the bacteria on lactose, dextrose, saccharose, and rafhnose, on the poly- 
saccharide inulin, and on the alcohols mannite and glycerin. The nutrient 
solutions were prepared as by Rogers and Davis (19 12), with the following 
proportions : 

Per cent 

Beef extract 0.4 

Peptone 1 . o 

Dibasic potassium phosphate 0.5 

Test substance 2.0 

In these experiments the age of the bacteria was not constant at the 
time of inoculation, for according to Rogers and Davis (19 12) this is not 
necessary. They say (page 20 of reference cited) : "In our own work 
no systematic investigation was undertaken to determine the constancy 
of the fermentation reactions, but all our observations tend to prove that 
the property of forming acid from carbohydrates and similar substances 
is not easily lost or acquired. One culture showing no evidence of ability 
to ferment saccharose was carried for one hundred generations, or a period 
of about one year, on a saccharose-agar. At the end of this period the 
culture still showed no fermentation of saccharose and the lactose fermen- 
tation remained unchanged." 

Rogers and Davis consider that acid formation is the most important 
factor to be observed in the study of lactic acid bacteria. In these studies, 
however, the writer observed, along with the acid development, the appear- 
ance of the media and whether or not gas was produced. 

The inverted-inner-tube method was used for the detection of gas. 
The cultures were incubated at room temperature for seven days. The 
acidity of the media was +1.5. The titration was made in duplicate 
with N/20 NaOH solution. The results of two studies of these bacteria 
when grown in the above solutions are given in tables 17 and 18 (pages 642 
and 643). The percentage of samples that showed growth in the two tests 
are summarized in table 19 (page 643). These figures are very much like 
those reported by Rogers and Davis (19 12), which they have assigned to 
the class generally known as the Bacterium lactis acidi group. 

Further study should be made in order to determine the strain of the 
Bacterium lactis acidi group to which these organisms belong. A few 
attempts have been made to study the various strains of this group, but 
thus far very little has been accomplished. 

CONCLUSIONS 

Direct absorption of metals may cause metallic flavor in dairy products. 

Bacteria may cause metallic flavor. Buttermilk in sterilized glass 

bottles developed the flavor in many cases. Of 241 samples of cream in 



628 Bulletin 373 

sterilized glass bottles, metallic flavor was produced in 79 by inoculation 
with metallic-flavored buttermilk; and of 157 samples of cream in ster- 
ilized glass bottles, which were inoculated with individual bacteria, 52 
showed metallic flavor. 

The organism that causes metallic flavor is a member or a strain of the 
Bacterium lactis acidi group. 

Except in the case of buttermilk, a high fat content of the medium 
is essential for the production of metallic flavor. 

Metallic flavor may develop in cream of either good or poor flavor. 

The indications are that enzymes may be a factor in the production of 
metallic flavor. 

High acidity of the medium is a necessary condition for development 
of metallic flavor. 

BIBLIOGRAPHY 

Brown, Leroy A. 

1912 Metallic flavor. New York prod. rev. and Amer. creamery 

35:226. 

Golding, John, and Feilmann, Ernest 

1905 Taint in milk due to contamination by copper. Soc. Chem. 
Indus. Journ. 24: 1285-1286. 

Harding, H. A., and Van Slyke, L. L. 

1907 Chloroform as an aid in the study of milk enzyms. New York 
(Geneva) Agr. Exp. Sta. Tech. bul. 6:41-82. 

Irish Homestead 

1913 A metallic flavor. In Chicago dairy produce 19:45:13. 

Melick, C. K. 

191 2 Metallic flavor theories. New York prod. rev. and Amer. 
creamery 35:430. 

New York Produce Review and American Creamery 

19 1 2 Metallic flavor. New York prod. rev. and Amer. creamery 

35:227. 

Rogers, L. A., Berg, W. N., Potteiger, C. R., and Davis, B. J. 

19 13 Factors influencing the change in flavor in storage butter. 

U. S. Anim. Indus. Bur. Bul. 162:5-69. 

Rogers, L. A., and Davis, B. J. 

1912 Methods of classifying the lactic-acid bacteria. U. S. Anim. 
Indus. Bur. Bill. 154:7-30. 



TABLE I. 



APPENDIX 

Acidity of Buttermilk Before and After Development of 
Metallic Flavor 



Sample 


Acidity before 

metallic 

flavor 

developed 

(per cent) 


Acidity after 

metallic 

flavor 

developed 

(per cent) 




0.67 
0.64 
0.67 
0.67 
0.67 
0.67 


0.73 
0.74 
0.81 


., 






0.74 

o.75 
0.72 


5 


6 







TABLE 2. Effect of Temperature on Development of Metallic Flavor 



Experiment 


Number of 
samples 

metallic in 
flavor at 
low tem- 
perature 


Number of 
samples 

metallic in 
flavor at 

room tem- 
perature 


Remarks 


I 

2 

3 

4 ■ • 

5 

6 

7 

8 

9 




4 


1 
1 
1 
1 
1 
1 
1 
6 
3 


Low-temperature sample more metallic in 
flavor than room-temperature sample 

Low-temperature sample more metallic in 
flavor than room-temperature sample 

Low-temperature sample more metallic in 
flavor than room-temperature sample 

Low-temperature sample more metallic in 
flavor than room-temperature sample 

Low-temperature sample more metallic in 
flavor than room-temperature sample 

Room-temperature sample more metallic 
in flavor than low-temperature sample 

Room-temperature sample more metallic 
in flavor than low-temperature sample 

None of the six were metallic at low- 
temperature 

Room-temperature sample more metallic 
in flavor than low-temperature sample 



629 



630 



Bulletin 373 



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Metallic Flavor in Dairy Products 



631 



TABLE 4. A Study of Milk and Cream at One Cornell University 
Station 



Sample 


Flavor 






When fresh 


When one day old 


lactis 


5 




Bad 




6 




Fair 




7 


Fair 


Bad 


+ 

+ 


8 




Fair 


11 


Good 


Fair 


12 




Bad 


+ 
+ 
+ 


13 


Good 


Fair 


14 


Good 


Fair 


16 


Good .... 


Bad 


21* 


Good . . 


Slightly metallic 

Slightly metallic 

Fair. . 




25* 


Fair 




27 


Fair 


+ 
+ 
+ 
+ 
+ 
+ 


28 






32* 


Fair 


Fair . 


33 




Bad 


36 


Bad 




39* 


Bad 


Bad 


40 


Fair 


Fair 


42 


Good 


Bad 


+ 


44 


Fair 


Fair 




46 


Fair 


Good 


+ 


48 


Fair 


Fair 


+ 


49 


Fair 


Fair . . 


4- 


50 


Fair 

Good 

Good 

Fair 

Fair 

Good 

Good 

Fair 

Good 






52 * 


Fair 




5=5 


Fair 


+ 


56 


Bad 




57 


Fair 




60 




+ 


61 




+ 


62 


Fair 


+ 


63 


Bad 


+ 









632 Bulletin 373 

TABLE 5. Effect of Formaldehyde on Metallic Flavor in Buttermilk 







Butter- 








Experiment 


Sample 


milk 
(cubic 
centi- 
meters) 


Formalin 
(drops) 


Age 
(days) 


Flavor 


I 


1 
2 


100 
100 


2 
4 




Metallic 




Metallic 


II. . 


1 
2 


100 
100 


1 
2 




Metallic 




Metallic 




3 


100 


4 




Metallic 




4 


100 


8 




Metallic 


Ill . 


1 


100 
100 


2 

4 




Metallic 




Metallic 


IV 


2 


100 
100 


2 
4 


2 
2 






Metallic 




3 


100 


6 


2 


Metallic 




4 


100 


8 


2 


Metallic 




5 


100 


10 


2 


Metallic 




6 


100 


12 


2 


Metallic 


V 


! 


100 


3 


2 


Metallic 




'2 


100 


6 


2 


Not metallic 






100 


9 


2 


Not metallic 




4 


100 


12 


2 


Not metallic 




5 


100 


15 


2 


Metallic 


VI 


j 


100 


5 


2 


Metallic 




2 


100 


10 


2 


Metallic 




3 


100 


15 


2 


Metallic 




4 


100 


20 


2 


Too much formalin 




5 


100 


25 


2 


Too much formalin 




6 


100 


30 


2 


Too much formalin 


VII 


1 


100 


2 


2 


Metallic 




2 


100 


4 


2 


Metallic 




3 


100 


6 


2 


Metallic 




4 


100 


8 


2 


Metallic 


VIII 


1 


100 


1 


2 


Metallic 




2 


100 


2 


2 


Metallic 




3 


100 


3 


2 


Metallic 




4 


100 


4 


2 


Metallic 




5 


100 


5 


2 


Metallic 




6 


100 


6 


2 


Metallic 


IX 


T 












2 


100 


2 





Metallic 




3 


100 


3 


2 


Metallic 




4 


100 


4 


2 


Metallic 




5 


100 


5 


2 


Metallic 




6 


100 


6 


2 


Metallic 



Metallic Flavor in Dairy Products 



633 



TABLE 6. Effect of Formaldehyde on Bacteria in Buttermilk 







Butter- 








Experiment 


Sample 


milk 
(cubic 
centi- 
meters) 


Formalin 
(drops) 


Bacteria 
per 
loop 


Flavor 


V 


1 


100 


3 


90 


Metallic 




2 


100 


6 


60 


Not metallic 




3 


100 


9 


20 


Not metallic 




4 


100 


12 


15 


Not metallic 




5 


100 


15 


18 


Metallic 


VI 






5 
10 


520 
250 


Metallic 






100 


Metallic 




3 


100 


15 


150 


Metallic 




4 


100 


20 


100 


Too much formalin 




5 


100 


25 


75 


Too much formalin 




6 


100 


30 


75 


Too much formalin 



634 



Bulletin 373 






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Metallic Flavor in Dairy Products 



635 



TABLE 



Ratios of Numbers of Bacteria in the High-Acid Agar and 
in the Normal Agar 



Sample 



3 

4 

6 

7 

8 

9 

10 

11 

12 

13 

14 

Average 



55.305 



Buttermilk not metallic 


Buttermilk metallic 


in flavor 




in flavor 


High-acid 


Normal 


High- 


acid 


Normal 


agar 


agar 


agar 


agar 


1 to 


15.358 




t to 9,260 


1 to 


64.431 




1 to 45-735 


1 to 


88,675 




[ to 11, 024 


1 to 


13.132 




to 7 , 770 


1 to 


196,825 




to 168,605 


1 to 


51.184 




[ to 2,601 


1 to 


568,396 




to 243,205 


1 to 


148,936 




to 29,765 


1 to 


239.427 




to 1 , 508 


1 to 


24L755 




to 279,787 


1 to 


103,976 




to 46 , 688 



i4-922 



636 



Bulletin 373 



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ber of 
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tubes of 
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milk 


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Metallic Flavor in Dairy Products 



637 



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6 3 8 



Bulletin 373 



TABLE 



Production of Metallic Flavor by Inoculation 



Sample 


Judged by 


Ayres 


Middaugh 


Pickerill 


Luce 


Guthrie 




Slightly metallic. 


Metallic 

Metallic 

No 


No. 


Metallic 

No 


Slightly metallic 




No 


3 

4 

s 


No 


No 


No 


No 


Metallic 

Metallic 

No 


Metallic 

Metallic 

Metallic 

Slightly metallic. 

Metallic 

Metallic 

Metallic 

Slightly metallic. 

Metallic 

Metallic 

Metallic 

Metallic 

Metallic 

Metallic 

Slightly metallic. 

Metallic 

Doubtful 

No 


Slightly metallic. 


Slightly metallic. 


No 

Slightly metallic 

Slightly metallic 

No 


No 


Slightlv metallic. 

Doubtful 

Metallic 

Slightly metallic. 

Metallic 

Slightly metallic. 
Slightly metallic. 


7 


No. . . 


No 


No 


No 


No 


9 


Metallic 

No 


No 




No 






Strongly metallic 


No 




12 


No 




13 

14 

IS 


No . 


Slightly metallic. 
Slightlv metallic. 
Slightly metallic. 




Metallic 

Metallic 

No 


Strongly metallic 

Metallic 

Slightlv metallic. 
Slightlv metallic. 

Doubtful 

Metallic 

Metallic 

No 


Slightly metallic 
Slightly metallic 
Slightly metallic 
No 
No 


17 


Doubtful 


Doubtful 

No 

Slightly metallic. 

Doubtful 

No 


19 

20 


Strongly metallic 
Slightly metallic. 
No 


Slightly metallic 
Slightly metallic 













TABLE 12. Production of Metallic Flavor by Inoculation 



Sample 


1 




Judged by 




Ayres 


Middaugh 


Pickerill 


Luce 


Guthrie 




No 

No 

No 

No 

No 

No 

No 

No 

No 

No 

No 

No 

No 

No 

No 

No 

No 

No 

No 

No 

No 


No report .... 
No report .... 
No report .... 
No report .... 
No report. . . . 
No report .... 
No report .... 
No report .... 
No report .... 
No report .... 
No report .... 
No report. . . . 
No report .... 
No report .... 
No report .... 
No report .... 
No report .... 
No report .... 
No report .... 
No report .... 
No report .... 


No report .... 
No report .... 
No report .... 
No report .... 
No report .... 
No report .... 
No report. . . . 
No report. . . . 
No report. . . . 
No report .... 
No report .... 
No report .... 
No report .... 
No report .... 
No report .... 
No report .... 
No report. . . . 
No report .... 
No report .... 
No report .... 
No report .... 


Slightly metallic. . . 




2 


No 


, 


No 


No 






No 






No 


6. . 


Doubtful 


No 






No 


8. . . 


Slightly metallic. . 
Slightly metallic. . . 


No 














No 




No 


Slightly metallic 




No. 




Slightly metallic. . . 
Slightly metallic. . . 


No 




No 


16. . . 


No 




No 


No 


18. 




No 




No 


No 




No. . . 


No, 


Check 


No 


No, 









Metallic Flavor in Dairy Products 



639 



TABLE 13. Production of Metallic Flavor by Inoculation 



Sample 


Judged by 


Ayres 


Middaugh 


Pickerill 


Luce 


Guthrie 




No 

No 

No 

No 

No 

No 

No 

No 

No 

No 

No 

No 

No 

No 

No 

No 

No 

No 

No 

No 

No 




No report .... 
No report. . . . 
No report .... 
No report .... 
No report .... 
No report .... 
No report .... 
No report .... 
No report .... 
No report .... 
No report. . . . 
No report .... 
No report. . . . 
No report .... 
No report .... 
No report .... 
No report .... 
No report .... 
No report .... 
No report .... 
No report .... 




No 








No 






Strongly metallic . . 


No 






No 




Strongly metallic . . 


Strongly metallic. . 
Slightly metallic. . . 


No 


6. . . 


No 






No 


8. . . 




Strongly metallic . . 
Slightly metallic. . . 


No 






Slightly metallic 
Slightly metallic 
No 














Strongly metallic . . 




No 






Slightly metallic 






Slightly metallic. . . 
Strongly metallic . . 






No 




No 


No 






Slightly metallic. . . 
Slightly metallic. . . 
Slightly metallic. . 


No 


18. . . 


No 


No 










Slightly metallic. . . 


No 


Check 


No 


No 











TABLE 14. Production of 


Metallic Flavor by Inoculation 


Sample 


Judged by 


Ayres 


Midi laugh 


Pickerill 


Luce 


Guthrie 


2 

3 

4 


Metallic 

Metallic 

Metallic 

Metallic 

Doubtful 

Metallic 

No 


Metallic 

Metallic 

Metallic 

Metallic 

Metallic 

Metallic 

Slightly metallic. 

Metallic 

Metallic 

Metallic 

Metallic 

Metallic 

Metallic 

Metallic 

Metallic 

Metallic 

Metallic 

Metallic 

Metallic 

Metallic 

No 


Metallic 

Doubtful 

Metallic 


Strongly metallic 

Metallic 

Metallic 

Metallic 

No 


Metallic 
Metallic 

Slightly metallic 
Slightly metallic 


No 


6 


Bitter metallic. . 
No 


Stronglv metallic 

Doubtful 

Metallic 

Strongly metallic 

Metallic 

Metallic 

Strongly metallic 

Metallic 

Metallic 

Metallic 

Metallic 

Slightly metallic. 

Metallic 

Slightly metallic. 

Metallic 

No 


Metallic 
No 


8 


No 


Metallic 

No 






Metallic 

No 


Slightly metallic 




Slightly metallic. 




Metallic 

Metallic 

Metallic 

Metallic 

Metallic 

Metallic 

Metallic 

Doubtful 

Slightly metallic. 

Metallic 

No 


Slightly metallic 
Metallic 
Metallic 
Slightly metallic 


13 

14 


Doubtful 

Slightly metallic. 

Metallic 

No 


16 

17 

18 


Doubtful 

Slightly metallic. 
Metallic 


Metallic 

Slightly metallic 

Metallic 

Slightly metallic 

Metallic 

No 


20 

Check 


Metallic 

No 















640 



Bulletin 373 



TABLE 15. Production of Metallic Flavor by Inoculation 



Sample 


Judged by 


Hepburn 


Ayres 


Pickerili 


Luce 


Guthrie 






Metallic 

No 

Metallic 

Strongly metallic 
Doubtful 

Slightly metallic. 

Doubtful 

No 


Slightly metallic. 
No 


Slightly metallic. 
No 


Slightly metallic 
Doubtful 




No 

Metallic 

Metallic 

Metallic 

No 


3 

4 

5 


No, high acid. . . . 
Strongly metallic 
Metallic, high 


Strongly metallic 
Strongly metallic 

Slightly metallic. 

Metallic 

Slightly metallic. 
Slightly metallic. 
Slightly metallic. 

Metallic 

Metallic 

Slightly metallic. 

Slightly metallic. 

Doubtful 

No . 


Metallic 
Strongly metallic 


6 


Slightly metallic. 
Slightly metallic. 
Slightly metallic. 

Metallic 

Slightly metallic. 
No 


overripe 


&'....... 


Strongly metallic 

Metallic 

Metallic 

Slightly metallic. 
Strongly metallic 

No 

Strongly metallic 

No 


No, overripe 


9 


No, high acid . . . 
No 


Slightly metallic 




No 






No. . . 


Metallic 

Metallic 

No 


Slightly metallic 
Slightly metallic 


13 


Slightly metallic, 

high acid 

High acid, no. . . 
No 




No 


No . 


No, overripe 
No, overripe 
Metallic 


16 


No 

Metallic 


No 


No. . . 


No. . . 


Check 


Metallic 


Metallic 


Strongly metallic 



Metallic Flavor in Dairy Products 



641 



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642 



Bulletin 373 



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000000000000000c o e 1 



I ! I I I I I I I !! I I I I I I I I I I I 



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r- r^ i/iao coaoocxaeoooocoooaocoao r~oo oo m 

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Metallic Flavor in Dairy Products 



643 



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3 









CORNELL UNIVERSITY 
AGRICULTURAL EXPERIMENT STATION 



The Following Bulletins and Circulars Are Available for Distribution to 
Residents of New York State Who May Desire Them 



BULLETINS 



226 An apple orchard survey of Wayne County 
260 American varieties of beans 
283 The control of insect pests and plant diseases 
291 The apple redbugs 

295 An agricultural survey of Tompkins County 
307 An apple orchard survey of Ontario County 
313 The production of new and improved vari- 
eties of timothy 

316 Frosts in New York 

317 Further experiments on the economic value 

of root crops for New York 

318 Constitutional vigor in poultry 

320 Sweet-pea studies — III. Culture of the sweet 

pea 
325 Cherry fruit-flies and how to control them 
328 Hop mildew 

333 Control of two elm-tree pests 

334 A study of some factors influencing the yield 

and the moisture content of cheddar cheese 
337 The Babcock test, with special reference to 

testing cream 
341 Crop yields and prices, and our future food 

supply 



Sweet-pea studies — ■ IV. Classification of gar- 
den varieties of the sweet pea 

A continued study of constitutional vigor in 
poultry 

The tarnished plant-bug 

Endothia canker of chestnut 

Potato scab and sulfur disinfection 

The interior quality of market eggs 

Further experiments in the dusting and spray- 
ing of apples 

Two factors causing variation in the weight 
of print butter 

The cost of milk production 

Some important leaf diseases of nursery stock 

The home grounds 

Cost of producing milk on 174 farms in 
Delaware County, New York 

Woodlot conditions in Broome Countv, New 
York 

Woodlot conditions in Dutchess County, 
New York 

Dusting and spraying experiments with apples 

Forest legislation in America prior to March 
4, 1789 

The leaf blotch disease of horse-chestnut 



CIRCULARS 



Orange hawkweed, or paint brush 

The chemical analysis of soil 

Legume inoculation 

The improved New York State gasoline- 
heated colony-house brooding system 

The formation of cow-testing associations 

Milking machines: their sterilization and their 
efficiency in producing clean milk 

The fire blight disease and its control in 
nursery stock 

Wholesale prices of apples and receipts of 
apples in New York City for twenty years 



Some suggestions for city persons who desire 
to farm 

Peach cankers and their treatment 

Apple cankers and their control 

Poultry parasites; some of the external para- 
sites that infest domestic fowls, with sug- 
gestions for their control 

Methods of making some of the soft cheeses 

Fall spraying for peach leaf curl 

Dusting nursery stock for the control of leaf 
diseases 



Address MAILING ROOM 

COLLEGE OF AGRICULTURE 

ITHACA, NEW YORK 



644 




LIBRARY OF CONGRESS 
000 895 294 2 i 



